To investigate the influences of river bend geometry on flow structures, three-dimensional simulations were carried out. The influence of aspect ratio, channel sinuousness and curvature ratio were investigated. Simulation results show that with an increasing of channel aspect ratios, the streamwise variation of flow velocities decreases significantly, which is not the case for the spanwise direction. Simulation results also reveal the significant influence of the curvature ratio on the redistribution of primary flows. The streamwise variation of free-surface and bottom-wall velocities was compared and the phase differences between them was identified, which was described as anti-phase and out-of-phase patterns. Deep-water channels with an aspect ratio of 0.15 show significant phase-lag of flow velocities compared with channel geometry, this newly observed phenomenon implies the shift of the peak scouring point in fluvial river meanders. For the first time to our knowledge, the streamwise and spanwise variation of primary and secondary flow strength, as well as their spatial derivatives, are quantitatively provided, which are valuable for theoretical studies. It is also found that the widely adopted assumption that the streamwise velocity component is one order magnitude larger than the spanwise, is only valid for river bends with small curvatures and aspect ratios.

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